The present invention relates generally to interface devices between humans and computers, and more particularly to computer interface devices that provide force feedback to the user.
Interface devices are used extensively with computer systems in the implementation of computer-controlled games, simulations, and other applications very popular with the mass market of home consumers. In a typical implementation, a computer system displays a visual environment to a user on a display device. Users can interact with the displayed environment by inputting commands or data from the interface device. Popular interface devices include joysticks, "joypad" button controllers, mice, trackballs, styluses, tablets, pressure spheres, foot or hand pedals, or the like, that are connected to the computer system controlling the displayed environment. The computer updates the environment in response to the user's manipulation of a moved manipulandum such as a joystick handle or mouse, and provides visual feedback to the user using the display screen.
In some interface devices, haptic (e.g., tactile) feedback is also provided to the user, more generally known as "force feedback." These types of interface devices can provide physical sensations to the user manipulating the physical object of the interface device. Typically, motors or other actuators of the interface device are coupled to the manipulandum and are connected to the controlling computer system. The computer system receives sensor signals from the interface device and sends appropriate force feedback control signals to the actuators in conjunction with host events. The actuators then provide forces on the manipulandum. A local microprocessor can be used to offload some computational burden on the host. The computer system can thus convey physical sensations to the user in conjunction with other visual and auditory feedback as the user is contacting the manipulandum. Commercially available force feedback devices include the ForceFX joystick from CH Products, Inc. and Immersion Corporation, and the Sidewinder Force Feedback Pro from Microsoft Corporation.
One problem occurring in the commercially available force feedback devices is the free movement of the manipulandum, such as a joystick handle, when the device is not powered. For example, standard joysticks without force feedback capability typically include physical springs coupled between the joystick handle and the joystick base which provides a spring force on the handle and permanently functions to center the joystick handle in its degrees of freedom, causing the handle to be biased toward a straight and upright position and assisting in playing games. Force feedback joysticks, however, do not include such physical springs. This is because the forces provided by physical springs can interfere with the forces generated by the actuators of the force feedback device, which can greatly reduce the fidelity of generated forces. For example, if a vibration is to be output on the joystick, the force designer may not want a spring force from physical springs to be felt which would interfere with the vibration. However, a problem caused by the lack of physical springs in force feedback joysticks is that the joystick handles are not centered in an upright or other desired position. Although simulated spring forces can be output by the actuators to perform this centering function during normal joystick operation, it remains a problem when the joystick is not powered. For example, store owners or other vendors often display demonstration force feedback joysticks on shelves for users to test the way the handle grip feels. The demonstration joysticks are typically not powered, and since no physical springs are included, the joystick handles are tilted to one side, giving the undesired appearance of a faulty or broken joystick. In addition, spring forces on normal demonstration joystick models give the user an indication of how the joystick feels during normal operation when spring forces are present, which is not possible with unpowered force feedback joysticks. In other situations, the user may not be powering a force feedback joystick for some reason while playing a game, and the normal centering spring forces would not be present on the handle, thus inhibiting game play.
A different problem occurs in force feedback peripherals having a force transmission mechanism such as a cable drive. In some cable drive systems, an actuator transmits forces to a manipulandum by rotating a cable attached to a capstan drum, where the drum is coupled to the manipulandum. The cable typically rides along the end of the drum as the drum is rotated by the actuator. However, if the capstan drum is rotated too far, the cable can move off the end or side of the drums causing the transmission system to become inoperative. A different problem with the cable is keeping it correctly tensioned on the drum. When the cable has one or two ends that are rigidly attached to points on the drum, the assembly process for the system can become time consuming and expensive due to the requirements for tensioning the system. In addition, the cable typically requires re-tensioning as it becomes loose over time from use. Other problems occurring in commercially available force feedback devices include inaccuracies involved with sensing the position of the manipulandum and outputting forces on the manipulandum, such inaccuracies often contributed by plastic or other flexible components used in low-cost devices.